Fix passing double float complex arguments in sparc64.

Double float complex objects are not 16-byte aligned in either
gcc or solaris studio.  This patch makes gdb to not align double
float complex arguments in the dummy frame when calling a
function.

2014-02-11  Jose E. Marchesi  <jose.marchesi@oracle.com>

        * sparc64-tdep.c (sparc64_store_arguments): Do not align complex
        double float arguments to 16-byte in the argument slots.